Field of the Invention
The present invention relates in general to gain stages, and more particularly to a high speed gain stage having an analog input, high gain, and a determinable differential digital output using regenerative feedback.
Description of the Related Art
A low power precision analog comparator may be implemented using multiple gain stages. One or more input stages remove any common mode voltage and amplify a voltage difference between a pair of analog input voltages. A subsequent comparator gain stage compares the analog output voltages from the input stage(s) and outputs a corresponding differential pair of digital voltages. The differential pair of digital voltages should only have two opposite states, including a first state in which a first polarity is high while the second polarity is low, and a second state in which the first polarity is low while the second polarity is high. Additional stages may be included depending upon the desired digital output.
The comparator gain stage may be implemented as a conventional linear gain stage. A conventional linear gain stage, however, supplies digital output signals that can both be low, high, or somewhere in-between thus violating the requisite two-state digital output. In the conventional configuration, a small differential analog input may cause the conventional gain stage to provide an output that is proportional to the differential analog input, such that the outputs are analog rather than digital. Also, if the offset voltages of internal amplifiers are not the same, it is possible to have a differential voltage in which both outputs are either high or low. Any of these indeterminate digital output states cause at least two problems. First, the output(s) of downstream digital logic may be indeterminate. Second, the supply current of the circuitry can increase and even become excessive. It is desired that the differential pair of digital signals be well defined to prevent issues with down stream circuitry.